1. Field of the Invention
The present invention pertains to a drive system, comprising a drive shaft, which is or can be brought into torque-transmitting connection with a drive train, and a secondary drive system for transmitting torque between the drive shaft and at least one auxiliary unit. The drive system also includes at least one vibration damping device, which itself comprises a deflection mass carrier with freedom to rotate around a rotational axis and at least one deflection mass, which can shift position relative to the deflection mass carrier in at least one deflection plane. Upon the deflection of the minimum of one deflection mass from a home position with respect to the deflection mass carrier, the radial position of the minimum of one deflection mass changes with respect to the rotational axis.
2. Description of the Related Art
In drive systems of this type, various devices can be used as auxiliary units, including the compressors of air-conditioning systems, cooling fans, d.c. generators, etc. But it is also possible for certain functional areas of the drive system to be driven, as if they were auxiliary units, by the drive shaft itself, such areas including injection pumps or cam drives, which usually include a camshaft. Depending on whether a defined phase relationship between the movement in the auxiliary unit and that of the drive shaft is required, which is the case especially when the above-mentioned injection pump and cam drive systems are involved, or whether only the transmission of torque is required, the connection between the drive shaft and the auxiliary unit can have a greater or lesser degree of stiffness. When a high degree of transmission stiffness is required, spur gears toothed belts or chains can be used to transmit the torque. When a very high degree of transmission stiffness and a very precise phase relationship between the driving and the driven systems are not required, the torque can be transmitted by means of V-belts or timing belts.
It is known that various types of vibrational frequencies occur in systems of this type, in which internal combustion engines are often used as drive units. For example, in the case of four-cylinder, four-stroke engines, the ignition frequency is equal to twice the rpm""s of the crankshaft, because two cylinders fire for each revolution of the crankshaft. The situation is similar for injection pump systems. Here, too, two injections occur per revolution of the crankshaft, but they are phase-shifted with respect to the ignition sequence. All these frequencies are transmitted to the auxiliary unit via the more-or-less stiff connection between them. Because, for cost reasons, auxiliary units of this type are usually lighter in weight than the internal combustion engine itself or represent comparatively sensitive systems, the rotational irregularities transmitted to them can cause damage to them or lead to a decrease in their life-span, especially in cases where the connection between the systems is comparatively stiff. The transmission or transfer elements, i.e. V-belts, can also be excessively loaded.
To reduce the transmission of vibrations from the motor to the auxiliary units, it is known that, for example, an elastic coupling can be integrated into the pulleys or wheels of the auxiliary unit driven by a V-belt or a chain to provide for some relative movement between the pulley driven by the belt or chain and the pulley connected to the shaft of the auxiliary unit. The elastic coupling often used for this purpose is effective only for a certain frequency range or at a certain critical natural frequency. It is not possible for such elastic coupling to damp vibrations over a wide range of frequencies.
DE 198 31 159 discloses a system in which the crankshaft, for example of an internal combustion engine, is connected to a pulley. In this area where the crankshaft is connected to the pulley, a so-called speed-adaptive xe2x80x9cextinguisherxe2x80x9d is also provided, in which the centrifugal forces of various masses change in response to change of rotational speed to help decrease the vibrations. Vibration-damping devices of this type can be tuned to operate at certain frequencies.
It is the task of the present invention to improve the drive system of the general type in question in such a way that, by means of simple components which occupy little space, vibrations or vibrational excitations (frequencies) can be suitably reduced.
According to the present invention, at least part of the vibration-damping device is integrated into part of the secondary drive system.
As a result of the present invention, a degree of system integration is achieved in which, through the intermeshing of the various system areas, namely, the system area comprising the vibration-damping device and the system area comprising the secondary drive system, various components can assume a double function. This simplifies the design and reduces the size of the machinery, and at the same time it allows the vibrations to be reduced precisely in the area where vibrational excitations are especially critical.
According to an especially preferred aspect of the present invention, it is possible for the secondary drive system to comprise at least one auxiliary drive wheel, which can be rotated by the drive shaft, and for at least part of the vibration-damping device to form at least a part of the auxiliary drive wheel. By allowing the deflection mass carrier to form at least part of the body section of the additional drive wheel, different system areas can be fused both functionally and/or structurally.
Especially when, as discussed above, a defined phase relationship is required between the drive shaft and the secondary or auxiliary unit to be driven by it, it is advantageous for the auxiliary drive wheel to be a gear wheel and for the outer circumference of the deflection mass carrier to be provided with spur gear teeth. As an alternative, it is also possible for the auxiliary drive wheel to be a chain wheel and for the outer circumference of the deflection mass carrier to be provided with teeth.
In an alternative design, it can be provided that the auxiliary drive wheel is a pulley, which has a belt-guiding section on at least one of its axial sides, and that at least one belt-guiding section comprises at least a part of the vibration-damping device. In a variant such as this, the functional or structural system integration or fusion can be achieved easily by providing at least one cover element, which covers a space in which the minimum of one deflection mass is held, on the deflection mass carrier and by designing the minimum of one belt-guiding section to comprise the minimum of one cover element. To provide reliable guidance for the belt which passes over the pulley, it is proposed that two cover elements be provided on the deflection mass carrier and that the two cover elements form two belt-guiding sections.
The degree of system integration can also be increased by designing the auxiliary drive wheel as a pulley with a roll body for the belt and by allowing the belt roll body to form at least part of the vibration-damping device. The deflection mass carrier, for example, can serve as the belt roll body.
Auxiliary units often operate at a speed different from that of the crankshaft. When the auxiliary drive wheel is mounted on a shaft of the auxiliary unit, the speed is often changed by providing the auxiliary drive wheel with an effective radius, i.e., the radius around which a belt or a chain runs, which is smaller than that of the drive pulley. So that sufficient room can be provided for the vibration damping device, however, it is proposed that the minimum of one deflecting mass be mounted in the radial area of or radially outside the effective radial area of the auxiliary drive wheel.
The auxiliary drive wheel can, for example, be rigidly connected to the drive shaft or to an input shaft of the minimum of one auxiliary unit. It is also possible for the auxiliary drive wheel to be a tensioning pulley for an endless transmission element and/or a deflecting pulley for an endless transmission element, which is mounted rotatably on a suitable support. In an arrangement such as this, the deflection mass carrier can be mounted rotatably on the support by way of a bearing arrangement.
Various designs are known for these types of vibration-damping devices or xe2x80x9cextinguishersxe2x80x9d, the damping characteristics of which adapt to the rotational speed. For example, it is possible for the minimum of one deflection mass to be connected to the deflecting mass carrier by at least two connecting areas a certain distance laterally apart so that the mass has a certain freedom of movement with respect to the carrier. Each connecting area in the deflection mass carrier has a first guide path arrangement with a summit area on the radially outward side, whereas the deflection mass has a second guide path arrangement with a summit area on the radially inward side and a connecting bolt, which is guided by and free to move along the first and second guide path arrangements.
In an alternative design variant, a deflection path assigned to the minimum of one deflecting mass can be provided on the deflection mass carrier, along which path an outside circumferential surface of the minimum of one deflecting mass can move, preferably with a rolling motion. The deflecting path has a summit area on the radially outward side and deflecting areas which extend out from this summit area, the radial distance of these deflection areas from the rotational axis decreasing with increasing distance from the summit area.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.